Method for the processing of measurement data in a gas friction vacuum meter and a gas friction vacuum meter equipped with a circuit for the practice of this method

Abstract

A method for the processing of values measured in a gas friction vacuum meter, in which the pressure is determined by the drag on a magnetically suspended free ball, by forming a first time value t n-1 by measuring the time required for N/2 periods of revolution of the ball, and a second time value t n by the immediately following measurement of the time required for another N/2 periods of revolution of the ball, determining a pressure value by comparing the two times values, repeating this pressure value determination of two time values after each period of rotation for the same number N of periods of revolution of the ball to a total of z determinations, and displaying the average of the pressure value determined Z times. To be able to determine the pressure with optimum measurement times and uncertainties of measurement, the ratio of N to Z is selected at approximately 4:1.

What is claimed is: 
     
       1. A method for measurement value processing in a gas friction vacuum meter, in which the pressure value is determined by the drag on a magnetically suspended free ball, comprising: forming a first time value t n-1  by measuring the time of N/2 periods of revolution of the ball and a second time value by directly following measurement of the time t n  of additional N/2 periods of revolution of the ball, comparing the two time values to determine a pressure value, repeating this pressure value determination from two time values after each period of revolution for the same number of N periods of rotation of the ball to a total of Z determinations, and displaying the average of the Z-times-determined pressure value, N:Z being as at least one of 3:1, 4:1 and 5:1.   
     
     
       2. A method in accordance with claim 1, in which N:Z is as 4:1. 
     
     
       3. A method in accordance with claim 1, in which the value for the duration of the period of revolution is selected small and corresponds to the time for one revolution of the ball. 
     
     
       4. A method in accordance with claim 1, in which the value for the duration of the period of revolution is selected small and corresponds to the time for a fraction of one revolution of the ball. 
     
     
       5. Apparatus for performing a method for measurement value processing in a gas friction vacuum meter, in which the pressure value is determined by the drag on a magnetically suspended free ball, comprising forming a first time value t n-1  by measuring the time of N/2 periods of revolution of the ball and a second time value by directly following measurement of the time t n  of additional N/2 periods of revolution of the ball, comparing the two time values to determine a pressure value, repeating this pressure value determination from two time values after each period of revolution for the same number of N periods of rotation of the ball to a total of Z determinations, and displaying the average of the Z-times-determined pressure value N:Z, being as at least one of 3:1, 4:1 and 5:1, the apparatus comprising: a magnetically suspended, rotating ball, a pickup coil associated with the ball, and   circuit means for processing the signal induced in the pickup coil, including a computer, and measuring time preselector circuit means coupled to the computer.   
     
     
       6. Apparatus in accordance with claim 5, comprising at least one additional pickup coil associated with the ball.